Explain the events which provide the comic relief in Chapter 6 ?

The next morning, the plantation learns of Eliza's flight. Shelby is angry, and Haley is furious. Mrs. Shelby, however, is glad and says "the Lord be thanked. Haley demands that Shelby give him some horses to search for Eliza andHarry. The slaves have a strategy to stall him, however. First, they find it "curiously difficult" to round up all the horses. Mrs. Shelby joins in as well, by defying her husband and telling the slaves to "Be careful of the horses; don't ride them too fast." A slave, Sam, understands his mistress' meaning and places a burr under the horse's saddle so that it bolts and throws Haley. Everyone involved in the horse throwing Haley finds this quite funny. It takes several hours to catch the horse, and Sam must first rub it down before Haley can ride it. Thus, the slaves outwitted the slave trader and bought much precious time for Eliza.